A free-field microphone is designed to measure the sound pressure in a sound field and compensate for the influence of its presence in the sound field.

A free-field microphone measures the sound pressure as it existed before the microphone was introduced into the sound field; in effect, maintaining free-field conditions.

A free-field microphone should be pointed towards the sound source, i.e. at an angle of 0 degrees incidence to the source.

A random incidence microphone is designed essentially to measure sound pressure levels in a diffuse sound field as they existed before the microphone was introduced into the diffuse sound field. At higher frequencies, the presence of the microphone in the sound field becomes more significant and will influence the measured sound pressure levels.

In general, the sound pressure around the microphone cartridge will increase because of reflections and diffraction. This pressure increase varies with different incidence directions. A random-incidence microphone is designed so that it's frequency response characteristics compensate for this pressure increase, assuming that the sound waves arrive at random from all directions.

G.R.A.S. Low-noise measuring systems can measure noise levels below the threshold of human hearing, e.g. from disk drives, computer equipment in general and in quiet rooms.

A quiet location can easily be subjected to intrusive noise when many otherwise "inaudible" devices are in use.

It therefore becomes important to know in advance (through accurate measurements) the noise contribution of quiet products when many of these are to be placed in quiet working environments.

Specially designed for difficult measurement situations, for example in high temperatures (up to 800 degrees C) or airflow.

The right-angle design makes the probe microphone particularly well suited for measurements on exhaust systems and other machinery in general, as well as for scanning surfaces such as loudspeaker cones and loudspeaker cabinets.

Its very small size, low weight and all stainless-steel construction, make the probe robust, easy to handle and simple to mount.

As with Outdoor Microphones, these G.R.A.S. Environmental Microphones are equipped with four-pronged anti-bird spikes on top of the windscreen. This prevents birds from perching on top of the windscreen when the microphone unit is placed outdoors for long-term unattended noise surveillance.

These microphones can withstand rain and operate over a wide range of temperatures over periods lasting from a few days to several weeks.

A window microphone is a useful tool for measuring community noise striking the facades of, say, hospitals, offices and dwellings.

It can also be used to provide a useful assessment of current or improved sound proofing in buildings continuously exposed to external noise, e.g. from road traffic.